P0440 Code: EVAP System Malfunction Causes and Fixes

Among the OBD-II trouble codes, the standard set every US car has used since 1996, a P0440 code is the vague one in a family of precise codes. A misfire code names a cylinder, but this one names the whole evaporative emission (EVAP) system and stops there.

That's why two shops can read the same code and quote two different repairs, and why a new gas cap can change nothing. The light is telling you the test failed, not what failed it.

What does a P0440 code mean?

P0440 means the evaporative emission system failed a check, and the computer stored the general code rather than one that names a part. If the code beside it is from outside this family, our check engine light codes page says what that code means.

The system exists because gasoline gives off vapor even while the car is parked. Instead of venting it, the car stores that vapor in a charcoal canister and later draws it into the engine to burn.

A purge valve lets the stored vapor into the engine, and a vent valve opens or shuts the canister's air side. The engine computer checks it all for flow and leaks, the way you'd squeeze a balloon to see whether it stays firm.

Can you drive with a P0440 code?

Yes, as far as the engine is concerned, because the EVAP system doesn't fuel or run it. You can plan the repair rather than the tow truck, unless one of the signs below shows up.

If you smell gasoline, that's the exception: fuel or vapor is getting out, and that's a fire risk, not an emissions problem. Nissan's recall for a corroding filler tube warned that fuel leakage near an ignition source could result in a fire.

Stalling is rare with this code, but a stuck-open purge valve can pull vacuum on the tank, and one recall says that can deform the tank or stall the engine. If it stalls or the fuel gauge reads oddly, read every stored code and get it looked at promptly.

Left alone, the engine runs as before, but the fault stays and a lit check engine light can fail a computer-read emissions test. We'd stop driving and get it checked soon if:

• You smell gasoline. Near the filler door, under the car or inside it, especially after a fill-up.
• The engine stalls or cuts out. Not typical of this code, so another fault may be stored with it.
• Fuel drips or the tank looks dented. A leak or a tank pulled in by vacuum, which needs a shop, not a cap.

What are the symptoms of a P0440 code?

The check engine light may be the only symptom you'll notice, because the system handles vapor, not the fuel the engine runs on. The car can drive exactly as it did the day before, which is part of why the light gets ignored.

The other sign worth taking seriously is a smell of gasoline, especially near the filler door or after a fill-up. It means vapor or fuel is getting out, as owners describe in federal complaints, and one traced a strong smell to a valve that had come off the tank.

The code itself doesn't change how the engine runs, but a stuck purge valve behind it can stall the engine. A misfire code stored beside it is a separate fault, as the common questions explain.

What causes a P0440 code?

Any part that holds or moves fuel vapor, from the gas cap to the purge valve at the engine. The gas cap is the part owners name most, but no carmaker document ranks the causes, so a new cap is a guess until it's been checked.

P0440 alone confirms none of them, because the code names the system, not the part. Most carmaker fixes were written for the more specific EVAP codes, which the related-codes section sorts out. Here are the six places owners and carmakers found it, from the filler to the engine, then the wiring.

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1. The gas cap

The cap seals the filler neck with a rubber ring, and if it's loose, cracked or missing, the system is open. The test then fails because the system can't hold its pressure or vacuum, the same way a balloon with an open neck won't stay firm.

Check it first because it costs you nothing, but check it once. Of the 35 owner complaints on this code, 12 name the cap, and some say the code came back after a new cap.

Chrysler updated the cap itself on several models and tells its technicians to run the leak test with the original cap in place. Audi's fix for a very small leak on some newer cars is to untwist the cap's seal, with no new part.

2. The filler neck and filler pipe

The filler neck is the pipe that runs from the cap you twist down to the tank. It sits behind the wheel, where road salt reaches it, so on an older car it can rust through while the cap is perfect.

This is where several owners found the fault after a new cap failed to fix it. Carmakers have filed fixes for filler tubes and necks on several models, and one corroding tube became a recall.

3. The purge valve and its hoses

The purge valve opens to let stored vapor into the engine, and its hoses carry that vapor from the canister. A valve that sticks open or shut, or a hose that splits or kinks, upsets the flow the computer expects and fails the test.

Carmakers have filed fixes here for a split hose, a misplaced tube and a kinked line, and only the kink may need a new valve. One owner replaced the purge valve for P0440 at their own cost, but you'll spend less if the hose gets looked at first.

4. The vent valve and the canister

The vent valve sits on the canister's fresh-air side and closes so the system can be tested. Dust, water or a spider's web in that fresh-air path can block it, and the canister itself can crack or fill with dirt.

If a shop blames dust, ask for the leak test before it sells you a canister. GM's fix on its pickups is a sealed vent valve, and it tells technicians to keep the canister unless it fails that test.

5. The leak detection switch

Some cars run the leak test through a small switch at the canister, which one carmaker calls the evaporative system integrity monitor, or ESIM. It senses whether the sealed system holds vacuum, and when it fails the whole test fails with it.

One owner had that switch replaced for P0440, and another was told a pressure switch at the tank was the problem. The carmaker wrote a procedure to make sure the right test is run first, so ask for the maker's test procedure by name.

6. Wiring and software

The valves are electric, so a loose connector can fail the test while every part you'd buy is fine. A Chrysler bulletin that lists P0440 by name fixes a connector and needs no parts.

Software is the other cause that needs no parts, and several recent carmaker bulletins naming this code are engine-computer updates. Ask the dealer to check your VIN before you pay for a part.

One leak the test can find

How do you fix a P0440 code?

Start with the cheap checks, and let a test, not a guess, choose the part you pay for. To fix a P0440 code, start by reading and saving every code, and the first three steps cost little or nothing:

1. Read and save every code. Write down P0440 and anything stored beside it, because P0441, P0442, P0446, P0455 or P0456 each narrows where to look.
2. Check the cap once, properly. Look at its rubber seal for grit, splits or a twist, refit it until it clicks, and drive a few days. If the light returns with a sound seal, the cap is less likely, though a shop can still pressure-test it.
3. Run the VIN. A dealer checks bulletins, software updates and recalls by VIN, and our free VIN checker lists the recall campaigns for your car's model year. On NHTSA's free recall lookup, a search by year, make and model shows the carmakers' bulletins. A VIN search shows only open recalls.
4. Ask for a smoke test or the maker's leak test. A smoke test pushes visible vapor into the system and shows where it escapes. If your car tests through a leak detection switch, ask for the maker's procedure before that switch or the canister is replaced.
5. Replace only what the test found. Clear the code after the repair and drive normally until the monitor reads ready again.

You can do steps 1 to 3 yourself, and step 4 is the one you ask a shop for, with our guide to reading a repair estimate for what else to ask. If you can smell fuel, skip the waiting in step 2 and go straight to step 4.

If the code comes back after the tested part is replaced, ask for the test again before you buy another part. One owner needed that after a new cap and then a new filler pipe.

How much does it cost to fix a P0440 code?

Often nothing, if the cap only needed refitting, and a recall pays for the software and, where needed, the purge valve on some 2012–2018 Focus models. The federal emission warranty also covers parts like these for two years or 24,000 miles from delivery, or three years or 50,000 miles in California-type states.

Past the cap, the leak test decides the bill. A revised vent valve on a 2015 Chevy Silverado 1500 runs $185–$342, parts and labor, at an independent shop, and a purge valve on a 2019 Honda Pilot $100–$160, parts and labor.

The vapor canister is the priciest part: with its purge valve on a 2014 Focus 5-door, it comes to $261–$545, parts and labor, unless a Ford recall covers yours. A connector or a software update is a short dealer job, and may cost nothing on a car still under warranty.

The leak test is billed first, because a shop has to find the fault before it fixes it. At the counter, ask for the test result, the hours and the rate on the written quote, and whether the test fee comes off if you approve the repair.

Will a P0440 code clear itself?

The lamp can go out by itself, but the stored code stays longer. The lamp may go out after three trips in a row in which the check runs and finds nothing.

The stored code can take 40 warm-ups to erase without the fault, and a warm-up is a drive that brings the engine up to temperature. A clear with a shop's scan tool leaves a permanent code behind, which only clears after the car's own test passes. If a loose or missing cap caused it, the lamp may go out once the car verifies the cap is secured.

Will a P0440 code fail an emissions test?

It can, in states that read the car's computer, and clearing it first doesn't help. A lit check engine light fails there, and erasing the code leaves the evaporative monitor "not ready", which some states also reject.

Only driving sets the monitor back to ready, because the check runs by itself when its conditions are met. Ask the shop how much driving your car needs after the repair before you go back for the test.

Is P0440 the same as P0441, P0442 or P0446?

No, P0440 is the heading, and the codes around it each name one fault inside the same system. A second EVAP code tells you where to look, and P0440 alone doesn't.

Cars can store two of them at once, and the second one is the useful clue. Here's what each neighboring code tells you about where the fault sits:

• P0441 is about flow. Vapor didn't move from the canister to the engine the way it should.
• P0442 and P0456 are hole sizes. The system leaked, and the number says roughly how big the leak was.
• P0446 is the vent valve. The valve was told to close and the car couldn't confirm that it did.
• P0455 is a large leak. Check the cap first. It's the cheapest part to rule out.

Is the P0440 fix different on a Jeep, Toyota or GM?

Partly, because some carmakers run the leak test through a switch at the canister and some through the vent valve. The code reads the same, but the part that runs the test differs.

Newer Toyota and GM cars usually log the same faults as the more specific P0455, P0456 or P0442, so on those makes the carmaker fixes are filed under those codes. Start from the code stored beside P0440, or in its place.

A few fixes are small enough to ask about before any part is ordered. Some Jeeps need only a connector secured.

P0440 on Dodge and Jeep

A leak switch at the canister runs the test on many Dodge, Jeep and Ram models. A parts notice says the newer leak test comes before that switch or the canister is replaced.

Chrysler's EVAP fixes on these brands start with small things, not a new canister. One is the filler tube on the 2023 Grand Cherokee 3.6L, and another an improved cap on some 2021 models, now out of warranty. The third, a connector secured on the 2019–2020 Wrangler, is the one case naming P0440.

Whatever the model, a newer bulletin tells dealers to test with the original cap on, then confirm the leak with a smoke machine. Ask for the same order at an independent shop.

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Common questions

Asked most often

Can a bad purge valve cause P0440?

Yes, a valve that sticks or a split hose can fail the test. Several carmaker bulletins point at a split, kinked or misplaced purge hose or tube rather than the valve.

Will a P0440 code cause a misfire?

No, the code itself doesn't cause a misfire. A misfire has its own code that names a cylinder, so treat one stored beside P0440 as a separate fault.

Where is the EVAP system?

It runs from the gas cap and filler neck back to the tank and the charcoal canister, with the purge valve at the engine. The diagram in the causes section numbers each part where it sits.

This article is general information, not advice about your specific vehicle. See the disclaimer.